[Feat] add unit test for conv2d in int32_t

Context

Add unit test for conv2d in int32_t.

Modified files

• `Test_ConvImpl.cpp``, add several learning methods;

Detailed

This test concerns a conv 7x7 with padding {3,3,3,3}, stride {2,2}, no dilation. The datatype used is int32_t to test integer conv making a comparison betwween Aidge inference result and CPP operator (from backend_cpp)